Accession Number : AD0717568

Title :   Unsaturated Helium Cooling Limits. (Summary of Liquid Helium-4 Boundary and Heat Transport Studies.)

Descriptive Note : Final rept. Oct 67-Oct 70,

Corporate Author : CALIFORNIA UNIV LOS ANGELES SCHOOL OF ENGINEERING AND APPLIED SCIENCE

Personal Author(s) : Linnet,Christian ; Purdy,Vance ; Chang,Y. W. ; Frederking,T. H. K.

Report Date : OCT 1970

Pagination or Media Count : 84

Abstract : The report summarizes studies of liquid He4-solid boundary conductances and liquid He4 cooling limits. Emphasis is on the final phase of the investigations concerned with cooling by means of unsaturated pressurized superfluid He II. Cooling limits arise from the destruction of superfluidity when He II locally is replaced by ordinary fluid. The limiting heat flux densities have been studied with a vacuum-insulated vertical tube ('zero mass flow' configuration), closed and heated at its lower end. The limiting heat flux densities were found to be a function of the system pressure and temperature. For a comparison, data have been taken also for saturated He II. The pressure range of the unsaturated liquid studies extended from 1 atm to supercritical pressures of about 3 atm. The temperature had a strong effect on the limiting heat flux density which increased toward a constant value of about 3 W/sq cm below 1.8 degrees K. In contrast to saturated He II studies, no maximum in the cooling limit was detected. The unsaturated liquid data exceeded those for saturated liquid by a factor of about 2. Theoretical calculations have been carried out for both, saturated and unsaturated liquid. (Author)

Descriptors :   (*LIQUEFIED GASES, HEAT TRANSFER), (*SUPERCONDUCTORS, COOLING), GALLIUM, HELIUM, SUPERFLUIDITY, SINGLE CRYSTALS, CRYOGENICS

Subject Categories : Thermodynamics

Distribution Statement : APPROVED FOR PUBLIC RELEASE